This is a spec-compliant version of RTCPeerConnection.getStats returning a promise resolved with RTCStatsReport, a maplike containing RTCStats dictionaries. Stats are being implemented according to the spec in a continuous effort for coverage to become good enough that the old getStats method can be deprecated. The old getStats (taking a callback as argument) is very different from the spec and riddled with goog-prefixed things.
Docs: https://docs.google.com/document/d/1Wc6a4o0PqTxIWD7LM_smA7Z0GZUTy6XOgr1qyS4M7hQ/edit?usp=sharing https://cs.chromium.org/chromium/src/third_party/webrtc/api/stats/rtcstats_objects.h https://developer.mozilla.org/en-US/docs/Web/API/RTCRtpReceiver/getStats